1. Technical Field
The present invention relates to an image forming apparatus and an image forming method, which perform transfer in a state where a transfer medium is gripped.
2. Related Art
In the past, with respect to an image forming apparatus, an image forming apparatus has been proposed which uses a transfer roller having a transfer medium gripping member which grips a leading end portion of a transfer medium (refer to, for example, JP-T-2000-508280). In the image forming apparatus described in JP-T-2000-508280, in a state where the leading end portion of the transfer medium is gripped by the transfer medium gripping member, the transfer medium passes through a transfer nip portion by rotation of the transfer roller, whereby an image of an image carrier is transferred to the transfer medium. According to this image forming apparatus, since the leading end portion of the transfer medium is gripped by the transfer medium gripping member, the transfer medium is reliably peeled from the image carrier after the transfer.
On the other hand, an image forming apparatus is proposed in which a transfer medium passes through a transfer nip portion by rotation of a transfer roller, whereby an image of an image carrier is transferred to the transfer medium, and if a leading end portion of the transfer medium passes through the transfer nip portion, the transfer medium is peeled from the image carrier by an air flow generation device, and thereafter, the transfer medium is attracted upward in a vertical direction and moves in a state where a transfer image surface thereof faces downward in a vertical direction, thereby being transported toward a fixing section by a transfer medium transport belt of a transfer medium transport section (refer to, for example, JP-A-2009-205131).
Here, in order to improve a peel property of the transfer medium from the image carrier after transfer, consideration can be given to applying the technology of gripping the leading end portion of the transfer medium, as described in JP-T-2000-508280, to the image forming apparatus described in JP-A-2009-205131. In this case, since the gripping of the leading end portion of the transfer medium is released before the transfer medium transport section, a nip portion end position in a transfer medium movement direction of the transfer nip portion, a transfer medium releasing position, and a transfer medium transport section starting position of the transfer medium transport belt, where the leading end of the transfer medium first comes into contact with it, are disposed to form a virtual approximate triangle. Then, the transfer medium which has passed through the transfer nip portion is moved in a movement pathway which approximately follows two sides of the virtual approximate triangle by a driving force at the transfer nip portion.
However, since the gripping of the transfer medium is released before the leading end portion of the transfer medium reaches the transfer medium transport belt, after the release of the gripping of the transfer medium, the transfer medium needs to be moved from the transfer medium releasing position up to the transfer medium transport section starting position with use of the middle portion of the transfer medium by the driving force at the transfer nip portion. At this time, since the transfer medium moves upward in a vertical direction, a position of the transfer medium becomes unstable. In particular, if a difference in velocity is present between a movement velocity of the transfer medium at the transfer medium transport belt and a movement velocity of the transfer medium at the transfer nip portion, a position of the transfer medium at the time of movement becomes more unstable. Therefore, there is a danger that the transfer image surface of the transfer medium which has passed through the transfer nip portion comes into contact with a member of the image forming apparatus, which is located vertically below the movement pathway of the transfer medium, so that the transferred image is disturbed. Also, as described above, since a position of the transfer medium becomes unstable, so that a position of paper at an outlet of the transfer nip portion cannot be maintained, there is a danger that the transfer image surface of the transfer medium comes into contact with the image carrier, so that displacement of the image occurs. That is, with only simple application of the transfer medium gripping technology described in JP-T-2000-508280 to the image forming apparatus described in JP-A-2009-205131, it is difficult to obtain an excellent image.